The Southeast Asian nation is the world's biggest exporter of nickel ore, refined tin and thermal coal and home to the fifth largest copper mine and top gold mine.

The ban aims to boost Indonesia's long-term return from its mineral wealth by forcing miners to process their ores domestically. But officials fear a short-term cut in foreign revenue could widen the current account deficit, which has undermined investor confidence and battered the rupiah.

"Starting at midnight on Jan. 12, 2014, raw ore definitely cannot be exported," Energy and Mines Minister Jero Wacik told reporters shortly after a marathon meeting with the president and cabinet ministers.

However, in one of his biggest economic policy decisions since taking office nearly 10 years ago, President Susilo Bambang Yudhoyono passed a last-minute regulation that will likely ease the ban's impact for major mining companies like Freeport and Newmont. Details of the regulations were to be released later.

"Not only Freeport and Newmont, but we have 66 companies that have said they will build smelters ... these (firms) will get a chance to export processed minerals," Wacik said.

"The energy ministry will later give more details on the levels of concentrate allowed."

Most of the companies expected to feel the impact of the ban are small domestic miners, numbering in the the hundreds, that cannot afford to invest the hundreds of millions of dollars needed to build a smelter.

Mineral shipments totalled $10.4 billion in 2012, or around 5 percent of Indonesia's total exports, according to the World Bank.

HALTING SHIPMENTS

The uncertainty over the ban has forced Indonesia's top copper producer, Freeport, to halt exports until the government provides clarity on which minerals can be shipped, a union official told Reuters.

"There will be no concentrate exports from Freeport Indonesia in Papua as long as there is no government policy providing certainty on concentrate exports," said union official Virgo Solossa, adding that the firm has not made a shipment from its port since Dec. 15.

Company spokeswoman Daisy Primayanti said Freeport continued to provide copper to its local smelter for use domestically.

Freeport, the country's dominant copper produce with 73 percent market share, last month warned an unrevised ban would cut output at its Grasberg mine by 60 percent and lead to layoffs of half of its 15,000 Indonesian employees.

Under the proposed regulation that was being reviewed by the president in the run-up to the deadline, Freeport, Newmont Mining Corp and other miners would still be allowed to export copper, manganese, lead, zinc and iron ore concentrate until 2017.

But nickel ore and bauxite exports worth more than $2 billion annually would still be banned, while coal and tin shipments would not be affected.

However, it was not clear whether the final regulation had been revised.

A major economic impact could make the ban a hot political issue in this year's legislative and presidential elections, especially if it sparks a wave of layoffs in the world's fourth most populous country.

Thousands of mine workers have already been laid off ahead of the ban, sparking protests in Jakarta.

"We call on all mining workers to prepare to go on the streets and swarm the presidential palace if the government goes ahead with the implementation of the ban," said Juan Forti Silalahi of the National Mine Workers Union in a statement earlier on Saturday.

Police have been stationed at ports and around mines to secure those places in case of public disturbances, said national police spokesman, Boy Rafli Amar.